Segue 1 - A Compressed Star Formation History Before Reionization

Abstract

Segue 1 is the current best candidate for a "first galaxy", a system which experienced only a single short burst of star formation and has since remained unchanged. Here we present possible star formation scenarios which can explain its unique metallicity distribution. While the majority of stars in all other ultra-faint dwarfs (UFDs) are within 0.5 dex of the mean [Fe/H] for the galaxy, 5 of the 7 stars in Segue 1 have a spread of $\Delta$[Fe/H] $>0.8$ dex. We show that this distribution of metallicities canot be explained by a gradual build-up of stars, but instead requires clustered star formation. Chemical tagging allows the separate unresolved delta functions in abundance space to be associated with discrete events in space and time. This provides an opportunity to put the enrichment events into a time sequence and unravel the history of the system. We investigate two possible scenarios for the star formation history of Segue 1 using Fyris Alpha simulations of gas in a $10^7$ M${}_{\odot }$ dark matter halo. The lack of stars with intermediate metallicities $-3<$ [Fe/H] $<-2$ can be explained either by a pause in star formation caused by supernova feedback, or by the spread of metallicities resulting from one or two supernovae in a low-mass dark matter halo. Either possibility can reproduce the metallicity distribution function (MDF), as well as the other observed elemental abundances. The unusual MDF and the low luminosity of Segue 1 can be explained by it being a first galaxy that originated with $M_{\mathrm{vir}}\sim 10^7$~M${}_{\odot }$ at $z\sim 10$.

12 pages, 6 figures, ApJ, Accepted

References in corpus (21)

• The MAPPINGS III Library of Fast Radiative Shock Models
• Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
• Beasts of the Southern Wild: Discovery of nine Ultra Faint satellites in the vicinity of the Magellanic Clouds
• Near-Field Cosmology with Metal-Poor Stars
• Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• Turbulent Structure of a Stratified Supernova-Driven Interstellar Medium
• Segue 1: An Unevolved Fossil Galaxy from the Early Universe
• The Destruction of Cosmological Minihalos by Primordial Supernovae
• Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies
• Chemically Tagging the HR1614 Moving Group
• Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
• Early turbulent mixing as the origin of chemical homogeneity in open star clusters
• Preserving chemical signatures of primordial star formation in the first low-mass stars
• Magellan/M2FS Spectroscopy of the Reticulum 2 Dwarf Spheroidal Galaxy
• Ultrafaint Dwarf Galaxies - the lowest mass relics from before reionization
• Abundance anomalies in metal-poor stars from Population III supernova ejecta hydrodynamics
• Star Formation in Ultrafaint Dwarfs: Continuous or Single-age Bursts?
• Ultrafaint Dwarfs - Star Formation and Chemical Evolution in the Smallest Galaxies

Cited by in corpus (18)

• Star Clusters Across Cosmic Time
• The Faintest Dwarf Galaxies
• The Pristine survey I: Mining the Galaxy for the most metal-poor stars
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• Dynamics of dwarf galaxies disfavor stellar-mass black hole dark matter
• A Common Origin for Globular Clusters and Ultra-faint Dwarfs in Simulations of the First Galaxies
• The chemical evolution of the Bootes I ultra-faint dwarf galaxy
• The Suppression of Star Formation on the Smallest Scales: What Role Does Environment Play?
• On the Metallicity and Origin of the Smith High-Velocity Cloud
• Metal Mixing and Ejection in Dwarf Galaxies is Dependent on Nucleosynthetic Source
• Enrichment in r-process elements from multiple distinct events in the early Draco dwarf spheroidal galaxy
• The Pristine Dwarf-Galaxy survey -- III. Revealing the nature of the Milky Way globular cluster Sagittarius II
• Toward $abinitio$ extremely metal poor stars
• Exploring Simulated Early Star Formation in the Context of the Ultrafaint Dwarf Galaxies
• The Orbit and Origin of the Ultra-faint Dwarf Galaxy Segue 1
• Predictions for Complex Distributions of Stellar Elemental Abundances in Low-Mass Galaxies
• CEMPlifying reionization
• Star Formation Histories of Dwarf Spheroidal and Dwarf Elliptical Galaxies in the Local Universe